# Why does iodine get oxidized to iodic acid and not periodic acid by nitric acid?

Nitric acid oxidizes iodine to iodic acid, $\ce{HIO3}$ and not periodic acid, $\ce{HIO4}$, which is of a higher oxidation state. This happens although other nonmetals are oxidized to their highest oxidation state. How can this be explained?

• Can u pls give a balanced chemical equation for the reaction of I2 with conc HNO3. – Yashwini Aug 21 '20 at 18:34
• @Yashwini Sorry. This was a long time back. I am majoring in a completely different field for more than three years – Aaron John Sabu Aug 21 '20 at 19:23

Nitric acid is not strongly oxidizing enough to get iodine to +7. Relativistic effects tend to make the $s$ subshell valence electrons more stable than the others in heavy atoms (http://www.annualreviews.org/doi/abs/10.1146/annurev-physchem-032511-143755), so to some extent iodine acts as if it has only five valence electrons. To pull out those last two electrons and get periodic acid, electrochemical oxidation is commonly used with a very high oxidation potential (https://en.wikipedia.org/wiki/Periodic_acid).